The essential oil obtained by steam distillation from medicinal plants of Cinnamomum cassia and Prunellae Herba. Analysis of essential oils were performed on GC/MS selective detector. Separations were performed fused silica capillary column. The carrier gas was ultra pure helium with a flow of 1 $m{ell}/min$ and the splitless injector temperature was set as $280^{circ}C$. The column temperature program was as follows: initial temperature of $70^{circ}C$ for 4 min, and increased by $2^{circ}C/min$ 70 to $100^{circ}C$ (held 2 min), After that the temperature was varied from 100 to $200^{circ}C$ at $5^{circ}C/min$ (held 20 min), increase to $280^{circ}C$ (held 5 min) at $10^{circ}C/min$, in a total run time of 73 min. Ten volatile flavor components were identified from C. cassia and ten volatile flavor components were identified from Prunellae Herba. Strong inhibition of growth of Vibrio parahaemolyticus was obtained with all doses of C. cassia tested. Moreover, antimicrobial activity of C. cassia occurred in a dose dependant manner.